#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
#include<math.h>
int main()
{
	int n;
	scanf("%d", &n);
	double sum = 0;
	for (int i = 1; i <= n; i++)
	{
		sum += sqrt(i);
	}
	printf("sum = %.2lf", sum);
	return 0;
}